Reland of [ObjC ARC] Converts ios/chrome/browser/ui/contextual_search:contextual_search to ARC.

ios/chrome/browser/ui/contextual_search/contextual_search_header_view.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IOS_CHROME_BROWSER_UI_CONTEXTUAL_SEARCH_CONTEXTUAL_SEARCH_HEADER_VIEW_H_
 #define IOS_CHROME_BROWSER_UI_CONTEXTUAL_SEARCH_CONTEXTUAL_SEARCH_HEADER_VIEW_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/contextual_search/contextual_search_panel_protocols.h"
 
 @interface ContextualSearchHeaderView
     : UIView<ContextualSearchPanelMotionObserver>
 
-@property(nonatomic, assign) id<ContextualSearchPanelTapHandler> tapHandler;
+@property(nonatomic, weak) id<ContextualSearchPanelTapHandler> tapHandler;
 
 - (instancetype)initWithHeight:(CGFloat)height NS_DESIGNATED_INITIALIZER;
 
 - (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
 
 - (instancetype)initWithFrame:(CGRect)frame NS_UNAVAILABLE;
 
 // Set the displayed text to |text|, with text in |followingTextRange| colored
 // gray.
 - (void)setText:(NSString*)text
     followingTextRange:(NSRange)followingTextRange
               animated:(BOOL)animated;
 
 // Set the diplayed text to |searchTerm|.
 - (void)setSearchTerm:(NSString*)searchTerm animated:(BOOL)animated;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_CONTEXTUAL_SEARCH_CONTEXTUAL_SEARCH_HEADER_VIEW_H_